When a hem is first formed in a textile work piece and later is sewn closed by a sewing machine, it is difficult to accurately form the beginning of the hem so that the depth of fold of the hem is the same at the beginning of the sewing run as it is at the end of the sewing run. In a situation where the work piece has a continuous edge that is to be folded over and sewn to complete the hem, for example the waist hem of a tubular knitted shirt, the fold that is being formed at the edge of the work piece will be a continuous fold about the circular waist edge of the shirt. It is important, therefore, that the end of the folded hem match up with the beginning of the folded hem as the sewing machine completes its cycle of operation, so that a continuous hem is formed.
A procedure that has been used in the past for forming a continuous folded hem about the circular edge of a textile work piece is to begin the folding operation during a pre-feed movement of the work piece before the sewing function is initiated. The edge of the work piece is placed under tension and is advanced through the sewing station with the needles and presser foot of the sewing machine raised out of the way and inoperative. The folding mechanism that is used to form the fold in the edge of the work piece is placed in operation so that the fold of the hem is formed for a short time period before the sewing function begins, with the edge portion of the work piece being turned under the adjacent body portion of the work piece. This pre-feed movement delays the start of the sewing cycle and thus allows the hem to be formed before the sewing function is started.
While the above-described pre-feed sequence accomplishes a fold in the work piece as it emerges from the folder, the presser foot, being raised and therefore inoperative, does not maintain the fold in the edge of the work piece as the work piece advances across the work surface of the sewing station. Likewise, the inoperative sewing needles do not perform their stitching function to sew the fold into the work piece. As a result, the tensioned edge portion of the folded hem tends to curl and to progressively unfold itself as it advances away from the folder, across, and beyond the sewing station during the pre-feed portion of the cycle of the system. The result of this phenomenon is that the depth of the overfolded portion of the hem that is sewn by the sewing machine is likely to be smaller and not as perfectly formed at the beginning of the line of stitching than it is at the end of the line of stitching. This tends to create a visual flaw in the hem and increases the risk of the textile piece becoming a "second" which is unacceptable to the potential purchaser of the work piece.
Thus, it can be seen that there is a need for a simple system for accurately establishing and maintaining the fold in a hem formed at and along the edge of a work piece during the pre-feed sequence of the sewing system, and before the presser foot and sewing needles are started for sewing the hem into the work piece.